Affiliation:
1. Leibniz‐Institut für Polymerforschung Dresden e.V. Hohe Straße 6 01069 Dresden Germany
2. Faculty of Chemistry and Food Chemistry Technische Universität Dresden 01069 Dresden Germany
3. Chair of Physical Chemistry of Polymeric Materials Technische Universität Dresden 01069 Dresden Germany
Abstract
AbstractHydrogels are usually depicted as a homogenous polymer block with a distinct surface. While defects in the polymer structure are looked into frequently, structural irregularities on the hydrogel surface are often neglected. In this work, thin hydrogel layers of ≈100 nm thickness (nanogels) are synthesized and characterized for their structural irregularities, as they represent the surface of macrogels. The nanogels contain a main‐chain responsiveness (thermo responsive) and a responsiveness in the cross‐linking points (redox responsive). By combining data from ellipsometry using box‐model and two‐segment‐model analysis, as well as atomic force microscopy, a more defined model of the nanogel surface can be developed. Starting with a more densely cross‐linked network at the silica wafer surface, the density of cross‐linking gradually decreases toward the hydrogel–solvent interface. Thermo‐responsive behavior of the main chain affects the entire network equally as all chain segments change solubility. Cross‐linker‐based redox‐responsiveness, on the other hand, is only governed by the inner, more cross‐linked layers of the network. Such dual responsive nanogels hence allow for developing a more detailed model of a hydrogel surface from free radical polymerization. It provides a better understanding of structural defects in hydrogels and how they are affected by responsive functionalities.